This invention relates to a manufactured granular substrate suitable for use as a carrier for chemical agents, as well as a method for producing a granular substrate. More particularly, this invention relates to a water dispersable, light weight manufactured granular substrate.
Generally, manufactured granular substrates are utilized as carriers for active chemical agents, such as for example herbicides or other pesticides. The carriers, with the active chemical agents, are utilized to distribute the active agent over a broad area. The carriers are generally inert compounds that, upon application, break down over time. Existing water dispersable carrier compositions have larger than desired particles sizes accompanied by high bulk densities of greater than 60 pounds per cubic foot. It is preferable to utilize a carrier with smaller granules and a lower bulk density in order to efficiently transport and distribute the required amount of active chemical agent without utilizing excessive amounts of inert carrier compounds.
In addition, conventional manufactured granular substrates often have a tendency to break apart thus creating handling and distribution problems. Granular substrates that resist attrition are preferred because they will not degrade and therefore maintain their particle size during handling. While resistance to attrition is important, the carrier compound must however breakdown or disintegrate upon exposure to water.
U.S. Pat. No. 5,078,779 discloses a binder composition for the granulation of dry, stable, particulate fertilizers. The composition generally includes a reactive carbonate and a reactive sulfate, in combination with a silicate strengthening agent and a water dispersing agent. Dolomite is disclosed as a carbonate source for the binder composition. The binder is used in conjunction with ammonium sulfate to provide a granulated fertilizer. In order to form the granulated fertilizer, the patent teaches the use of a reactive acid to initiate a reaction between the sulfate salt and the metal ion of the carbonate to form a complex salt.
A manufactured granular substrate having 10% to 100% plant fiber and 0% to 90% of a mineral filler is disclosed in U.S. Pat. No. 5,019,564. The substrate is formed by the agitated agglomeration of a fibrous slurry without the use of a binder. The plant fibers are generally 1 mm to 10 mm in length. The resulting substrate has a bulk density of about 20 to 42 pounds per cubic foot. The substrate is utilized as a carrier for active chemical agents. However, the substrate does not readily breakdown upon exposure to water. Additionally, the fibrous nature of the substrate can reduce the ability of the substrate to flow in bulk form.
U.S. Pat. Nos. 4,015,973, 4,954,134, and 5,228,895 all generally disclose the use of either limestone or dolomite in conjunction with a lignosulfonate binder in the formation of manufactured granular substrates. The agglomerated particles produced in accordance with the patents are either outside the preferred size and bulk density or are susceptible to degradation during handling.
Additionally, U.S. Pat. No. 5,242,690 discloses an inert manufactured granular substrate as a carrier for chemical agents. The granular carrier composition includes grain dust and a binder of either calcium or sodium lignosulfonate. The finished granular carrier exhibits a bulk density between 30 and 35 lbs per cubic foot.
Thus, existing manufactured granular substrates utilize either limestone or dolomite with other binding or reactive components to produce granular substrates as carriers for active chemical agents. The existing manufactured granular substrates are not of the desired size or bulk density. Also, some of the existing manufactured granular substrates have a tendency to breakdown during handling thereby changing the bulk density or creating distribution problems during application. Other granular substrates, produced from primarily plant fiber, have some desirable physical properties but fail to readily disintegrate upon exposure to water.
It would be an advantage to produce a manufactured granular substrate for use as a carrier compound for active chemical agents that has a bulk density of less than about 55 pounds per cubic foot at a relatively small particle size. A manufactured granular substrate having the noted properties is capable of delivering an appropriate amount of active chemical agent to a desired area while utilizing less inert material. Furthermore, smaller particle sizes provide a greater surface area for the chemical agent and result in an improved distribution or coverage of the desired area of application.
It would also be an advantage to produce a manufactured granular substrate that does not degrade during handling but breaks down when exposed to moisture or water. The resistance to attrition ensures the proper distribution of the active chemical agent upon application. Furthermore, the ability to disintegrate upon exposure to water is needed to provide the active chemical agent to the soil.